Combustion control apparatus



y.tenfiperature to pass througha maximum.

Patented Jan. 19, 1954 COMBUSTION CONTROL APPARATUS Waldo H. Kliever, Minneapolis, Minn., assigner to Minneapolis-Honeywell'Regulator Gompany, Minneapolis, Minn., a-corporation of Delaware Application December 18, 1950, .Serial-No. 201,330

12 Claims.

The present invention is yconcerned with a l vtemperature in the fuel burning ,apparatus and further apparatusgfor controlling the flow of one of the products of combustion so that it is lpos sible to adjust this flow to maintain the burner temperature at a maximum.

It has been found that when there is a constant flow of one of the products of combustion into aburner, i. e., ythe air or fuel, the variation of the other of the components from a minimum value to a maximum value `will cause ,the burner It is. this characteristic which is used in the present apparatus for controlling fuel or air ilow of a combustion process to maintain Va maximum temperature. small increments, it is possible to feel the'way adjustments must be made bythe apparatus in order that a maxi-mum temperature be maintained.

It is therefore an object of the present'invention to provide an apparatus for maintaining 'a maximum temperature in a fuel consuming apparatus.

By cyclically varying the ow byy Another object of the present invention is to I provide a combustion process control apparatus wherein one of the components of the combustible mixture 'is varied to a point necessaryl to maintain maximum combustion temperature.

Still another object of the present `invention is to provide a control apparatus wherein one of the components of ay combustible mixture is cyclically varied to cause a. cyclic variation in the burner temperature .to obtain a control signal for adjusting the mixture.

A 'further object of the present invention is to provide a control apparatus wherein a maxil kperature responsive .bridge which is maintained eectively balanced while the bridge is producing `a signal foroausingsaid apparatus vto maintain the ,combustion process temperature at a maximum.

I hese and .other objects of the present invention will be understood upon considering the following specification and the appended 4drawing `0f which:

Figure 1 shows schematically one arrangement .in which `the control apparatus may be constructed; and

Y V.ligure 2 shows graphically the principle which permits the operation of the present apparatus.

Referring to Figure '1, the numeral l0 represents a furnace of ,any desired type wherein is located suitable burner mechanism. Supplying fuelto the furnace :I0 `isa'conduitand vvalve assembly Il -which conducts the fuel to a suitable mixing :uniti 2 :wherethe fuel is mixed with primary air .andthentoa burner positioned within the furnace 1.0. Secondary air or any other suitable o-medium lis supplied to the mixing unit I2 through Ya conduit I3. The combustion process will take Vplaceabove ithe burner rand the com- :bustion ,fproductsgwill pass ythrough va plurality of heat exchange .conduits i4 and from there out through an-.exhauststack I5.

For modulating lthe rflow of the secondary air through the Vconduit `1.3,-a damper 20 is provided. This -damper is arranged to be Apositioned by a two phase reversible motor '21 -having an amplier phased winding 2l-a anda line winding 2lb which .w'henzenergized will cause rotation of the motor -a direction depending on the phase re- :lationof the voltages'onthe windings. The motor 121 is connected to the damper 2B through a suitable .driving means .22. A pair of power line connections 23 and ,24 are connected to a reverand 2.4. f The operating energy for the switch- Ving mechanism 25 isfobtained from a cam 40 which -operates'upon a follow up member 4I. The cam 40 is .arranged to be driven by a continuoursly operating motor 42 which, through a .suitable Vdriving `connection 4'3, drives a further 10am .4.4.

The cam `4.4 has riding thereon a cam follower member 45 which is mechanically connected to a damper member 45, the latter of which is arranged to be cyclically opened and closed, or varied, with the operation of the motor 42 and the resultant driving of the cam 44. Each of the cams it and 44! have a semi-circular dwell section and are so arranged that the respective followers will be in one position for half of a revolution of the cam and in another position for the subsequent half.

For sensing the temperature of the nre within the furnace it there is provided a suitable temperature responsive resistance element 50 which is connected as one leg of a bridge network I. The power for the bridge network 5I lis supplied by a transformer 52 and the network, in addition to the resistor 5U, comprises further, a pair of xed resistors 53 and 54 and a reset rheostat 55.

rEhe output of the network 5l is connected to ythe input of a pair of amplifiers 6l! and 6I both of which may be of the discriminator type which supply an output which varies both in phase and amplitude depending on the direction of unbalance of that input circuit and the amount of unbalance thereof. Such an amplier is shown and described in the Albert P. Upton Patent No. 2,423,534, issued July 8, 1947. The output of the amplier 5d is fed through a pair of leads 52 and 53 to the amplier winding 21a. of the reversible motor 2l. The output of the amplifier 5i is connected by a pair of leads 64 and 65 Ato reset motor 56, said reset motor being of the reversible type and being arranged to drive the slider of the potentiometer 55.

Operation In considering the operation of the present apparatus, reference should first be made to Figure 2. Figure 2 shows in graphical'form what happens to the burner temperature as the fuel yor air supply is varied from a minimum value to a maximum value while the other component, air or fuel, depending upon which is varied, remains flowing at a substantially constant value. The temperature curve is represented by the curve 75. Fuel or air supply is plotted on the abscissa of the graph and the furnace temperature is plotted on the ordinate of the graph. Obviously the configuration will vary, depending upon the types of fuel used and whether fuel or air flow is varied.

Assuming that the air supply is being varied with the fuel supply being substantially constant and assuming that the air iiow is represented on the graph of Figure 2 as at the point 1l, the furnace temperature will be represented by the intersection of a vertical line drawn from the point ll and will intersect the temperature curve 'it at l2. Inasmuch as it is desired that the furnace temperature be maintained at a maximum value, which is by Figure 2 considerably higher at point 13, it is desired that a corrective signal be obtained and used to change the air flow so that the maximum temperature at point 'i3 will be obtainable. Referring now to Figure l, it will be assumed that the damper 2i? is in the position in which it is shown upon the drawing and that the cycling motor 42 is continuously operating. The cycling motor 42 is arranged to drive the associated cams 40 and cl2 at a speed of approximately 12 R. P. M., or one revolution every five seconds. The rotation of the cam 44 will cause the follower 45 to operate upon the cycling damper 46 so that there will be a resultant change in the air ow to the furnace lil. When the follower 45 is on the raised portion of the cam 44 the cycling damper 46 will be opened and there will be a greater amount of air flowing into the furnace. When the follower 45 is riding on the down dwell portion of the cam 44, the cycling damper will be effectively closed so that the air flow will be decreased.

As the cycling damper 45 operates, assuming that the flow control damper is remaining stationary, the secondary air supply will be effectively varied between the points and 'l5 on the airsupply temperature curves shown in Figper minute will,

yure 2. The vertical projection of these points will cause an intersection of the temperature curve l0 at v points 7'! and i8. The horizontal projection upon the temperature axis of the points of intersection 11 and 18 on the temperaturecurve TB indicate that the temperature in the furnace will vary from point 19 to 3U. Inasmuch as the cycling motor 42 is continuously operating there will be a cyclic variation in the temperature of the furnace and this cyclic variation is as represented by the curve 2l. Assuming that the air flow starts at the point shown on the air supply axis 'Il and decreases to point 'I5 and then increases to 16 and then back to H, there will be a particular phasing of the temperature variation in the furnace In and, as shown in drawing in Figure 2, will be a Cosme wave.

Referring back to Figure 1, it will be noted that the cycling motor 42 drives the cam 40 which in turn, through the follower 4i, operates upon the switching mechanism 25. The rate of operation of this switching mechanism is the same as the rate of operation of the cycling damper 46. The operation of the switching mechanism 25 will cause the reversible motor 2l to have its line phase winding reversibly energized twelve times per minute.

Considering now the fact that the burner temperature is varying in a cycling manner at 12 cycles per minute, it is desired to coordinate this temperature variation with the cyclic Variation on the line phase winding 2lb of the motor 2l. This is accomplished by the temperature respon- `sive resistance element 50 whose resistance is arranged to vary with changes in the furnace temperature. The network 5| will accordingly have an electrical output which varies at a cyclic rate and this will be fed from the network through the conductors 82 and 83 into the input of amplier 60.

Assuming that the bridge 5l is balanced, the output voltage will vary at the rate of 12 cycles per minute and the alternating current phasing of the 60 cycle per second power supply will be reversed at this rate of 12 cycles per minute. This reverse phasing of the 60 cycle signal at l2 cycles when coordinated with the switch mechanism 25, operate to drive the motor 2| in a direction to increase the air supply. In other words, during the half cycle of the 12 cycle per minute signal when the output phasing of the amplifier 65, when compared with the phasing of the line signal fed through the switching ymechanism 25 is acting upon the motor 2 l it will cause the motor to be driven in a direction to increase air flow. On the following half cycle of the 12 cycle per minute signal, the change in resistance of resistor 52 will unbalance the bridge in the opposite direction and the output phasing of the ampliiier E0 will be reversed. At the same time; the operation of uic swaterungr'mechamsmV ZEWill reverse theline phasing of the-A2 G2 power signal on' the`V mjotor 25H so tliatlthe'net result of thesignaIrom-the amplifier and'frorn the line will cause the motor' 2 if tc-continue tc-rotate-in the same'direction to'increase air supply; The cam d is so mounted'that' the-operationoi'the switching meclianisrn` flags' bel'iindthel operation of^ damper' i'bythefsa'me amount' of time as the lag inthe response ofresistor 505i Stating this in'slightly different language, the ampl'iiier Sii' will have an output signal which will be 6i) cycles per second. Whenfthe temperature oi?`A the burner is not at a" maximum, and if the bridge 17 is effectively balanced', the yphasingV of this 60 cycle per second signal willoe reversed every time the cycling damper opens and closes andthe temperature of resistor 5&31 increases and: decreases' due to thefact that the bridge 5l' isl unbalanced rst in one direction and thenyin' the other.v The frequency of this phase reversal will be 12 cycles per minute as the cyclingdamper is operated at a ratev of 12 cycles per minute.l It should be noted thatA 'there' is no positive synchronization of the-12 cyclel per minute signal with the 60 cycle per second signal: If the 60 cycle per second signal which has its phase reversing at a rate or" 12 cycles per minute is fed from the amplifier to the amplifier Winding 2id ,off motor 2i, the 50 cycleV signal will cause the motor to run in one direction during one-half cycle of the 12 cycle per minutev signal or when the 60 cycle per second signal is of a iirstl phase 6., ofnetvrorkl 51' is'sensediand responded to so that motor* 66` adjusts' rheostat 55 to maintain the networkxilv in an efectivelybalanced condition so" that the cyclic variations' of the temperature will cause' the 6G cycle modulated wave to reversein phase every haiiy cycle. While the temperature off the furnace is displaced from the maximum and the motor 2i is changing the air Y supply, the reset motor S6 will-be readjusting the with the phasing ofthe line winding 2 ib'remaining'xed. On the subsequent half-cycle oi the 12 cycleper minutesignal, the phase of the 60 cycle per second signalon the amplifier winding of the-motor will reverse and if'the line winding lbV has the same phasing,` the'rn'otor will revverseits direction of operation'. It is desirable, however, to cause the motor to rotate in the sarne direction when the phasing of the 60 cycle signal reverses on the output of the network 5|'. To do this, the switch 25 is effective to reverse the line phase winding energization every one-half cycle of the 12 cycle per minute operation and thisY is synchronised withvthe phase reversals from'the` amplifier t@ or the network 5i. When this is done, it is possible to maintain the net 60 cyclephase relation between the amplifier winding Zia and the line windingv 2lb of they motor the same so that rotation ofthe motor will be in one direction. TheV motor will" operate ina direction to increasethe' air'supply by movement ofthe damper 2t.y f

The increased air supply will cause an increase in the temperature oft the lire and of theresistor i. rihis-increasein tempera-ture 'of .resistor 5t' will imbalance' the network 5i and this' unbalance, without further adjustment of the network 5i, will result' ini the'l2 cycle variations in bridge output' being a modulated 60 cycle phase. This modulated' 60' cycle signal of one 60 cycle' phase when ampli'ed andA applied to-motor 2l with the reversing of the'phasing of Y the line phase winding 2lblwillf tend to cause the motor 2! to oscillate about ay fixedr pointv in accordance with the 1'2v cycle variations because ofthe operation of the line phase reversing'switch 25. To correct for this, the amplifier Sli andr reset motor 65' are provided.- Thereset motor 6e'- is arranged to drive the slider ofth'e rheost'at' 55 at a relatively slow-speed sol that' the motor" 56 will not" try to followv the; I2 *cycle variations in the'y network 5T. However; tli'el average balance rh'eostat'v 55?' to maintain the network 5i eiiectively balanced. The operation ofthe reset motor 6Fl may be considered in slightly different languageA by recognizing first that iithe network 5l is considerably unbalanced, the. l2'cycle per minute "Jau'iat'ion` in =the temperature resistor 5i); due' toi operation of the damper 45,

will' not be sufcient-tcl-cause a phase reversal'in the`60`y cycle per'second output signal of the networlif 555i Thus; the phase of the signal fed to motor 66fromlamplier 6I will remain constant and4 the' motor 65. willoperate in one direction. As-then'etwork 5I approaches balance, the cyclic variation-of resistors@ will cause thelv phasing of the output'ofthe network to reverse for a time period` depending upon how far the network is unbalanced in the opposite direction the resistor Et. If the time period or unbalance is greater'with one phase of unbalance than for phaseunbalance ofthe opposite sense, the phasing which 1s in existence for the longest period ofv` timefwill cause tliernet energization and rotation of motor @Ci to be in a direction which will tendtov eliminate the time period diie'renee be tween the unbalance on either side of the main balance' point of the network.

The-.apparatusw-iilcontinue to operate in this manner until such time as the motor 2i has moved-the'damper Zti to point so that there is no longer any` cyclic variation in the temperature within' the furnace.

will cause the air ii'ow to vary between the points 9i and' 92. It will: be noted that the vertical projections to the points Si and 92 to the temperature vcurve 'lindicate they intersect the temperature curve at substantially the same values on either'side of the maX-imunrtemperature peint gi'zation of vline winding 2li b reversed periodically;

the motor 21 willl either have a very small hunt about point ifthe sensitivity of the system is high or remains stationary if` the 'system senn sitivityv is low.

I-n the event that the air suppl-ffy should be too' great, for example at point it@ as shown in the graphof Figure 2', it is desired the motor 2l bel driven'- in the reverse' to cut down theairsupply. If the average air supply is at thev point i60, and the cyclic darner 461 is' being operated, the air supply will be varied' between-points itil and E82 which points, when projected to the curve 'lili will produce a temperature output' curve substantially' as shown at m3; In the present. situation, starting with the" air' flow. at' point. we, ciosing'the damper :it tot point' liliA and then: opening the saine to point: W2 and: thence back tol iliwillcause the output: wave; m3. toil bel effectively` reversed from. theph'asing which is obtained; when' the air This air supply point.. referring toFi'gure 2; will be' represented vby the point 9%". The cyclic operation or the damper sgi supply is less than that necessary to produce maximum temperature. The resultant 12 cycle per minute modulation of the network will cause the output thereof to vary cyclically and appear as a 60 cycle signal which is reversing in phase every half cycle of the l2 cycle modulating signal. This signal when applied to the amplifier winding Zia and when combined with the line signal fed through the switching mechanism 25 will drive the motor El in a direction to decrease air supply. The motor il! will continue to operate until such time as the air supply at its mean value is approximately at the point S0 shown upon Figure 2.

In the event that the quantity of fuel or the type of fuel fed to the mixture unit i2 in the furnace it should be varied, it will be obvious that the maximum temperature of the furnace will vary and may require a different quantity of air supply in order to obtain a maximum temperature, inasmuch as any type or quantity of fuel in the air supply therefore is varied will produce a temperature curve upon combustion comparing to that of Figure 2, the apparatus will always adjust the control damper 2li so that the furnace temperature will remain at a maximum. To compensate for time lag in the system and to synchronize the temperature measurement with the cyclic operation of the damper d5, adjustment of the relative position of cams dit and ill on their driving shaft 43 is necessary.

It should be understood that while the apparatus is shown adjusting air supply with the fuel supply being assumed constant, the apparatus would work satisfactorily if the air supply were constant and the fuel supply were cyclically varied. Further, the cyclic variation can be made in one of the elements used in the cornbustion process while the flow control can be made on the other of the components of the combustion process. Further, the apparatus is for use in any type of combustion control such as a combustion engine or other similar apparatus.

While many modifications will be obvious to those skilled in the art, it is intended that the scope of the present invention be limited solely by the appended claims in which I claim:

l. Combustion control apparatus comprising, fluid flow control means, fluid flow cycling means for continuously cycling said iiuid flow, a balanceable electrical network having therein a resistor responsive to combustion temperature and the cyclic variations therein caused by said cycling means, said network having rehalancing means, discriminating amplifying means connecting said network in controlling relation to said fluid flow control means, and reversible electric switching means actuated by said cycling means controlling the direction of operation of said fluid flow con trol means with said amplifying means.

2. Combustion control apparatus comprising, fluid flow controlling means, fluid flow cycling means for continuously cycling the fluid iiow, a balanceaole electric network having therein a resistor responsive to combustion temperature and the cycling variations therein caused by said cycling means, discriminating amplifying means connecting said network in controlling relation to said fluid flow controlling means, reversible electric switching means actuated by said cycling means and controlling the directionof operation of said fluid flow controlling means with said amplifying means, and a slow acting reversible Velectric motor means connected to said network to rebalance said network to a balanced condition after a period of time longer than the time of each cyclic operation of said cycling means.

3. In control apparatus for a combustion process where variations in a fluid flow will cause combustion temperature to pass through a maximum value, the combination including :uid ow regulating means, temperature change responsive apparatus comprising a rst device adapted to respond to combustion temperature and a second device effective slowly to balance the effect of said first device so that said temperature change responsive apparatus is responsive to the rate and direction of change of combustion temperature, means for cycling the fluid flow, and means including switching means controlled by said temperature change responsive apparatus for adjusting said fluid flow regulating apparatus until the cycling of the uid flow causes no appreciable change in the combustion temperature.

4. In control apparatus for a combustion process where variations in a fluid iiow will cause combustion temperature to pass through a maximum value, the combination including fluid ilow regulating means, temperature change responsive apparatus comprising a rst device adapted to respond to combustion temperature and a second device effective slowly to overcome the effectof said first device so that said temperature change responsive apparatus is responsive to the rate and direction of change of combustion teinperature, means for cyclingthe iiuid flow, means controlled by said temperature change responsive apparatus for adjusting said fluid new regulating apparatus until the cycling of the fluid now causes no appreciable change in the cornoustion temperature, said last named means comprising motor means having a pair of control windings, one of which is lenergized oy said change responsive apparatus and the other of which cyclically reversed in phase energization at a rate corresponding to the rate of cycling of the duid flow.

5. In control apparatus for controlling the relative supplies of fuel and air to a combustion proeess comprising, means for controlling the supply of fuel to the combustion process, means including a reversible motor for controlling the supply of air to the combustion process, said motor having rst and second energiaation windings, a source of voltage, means including a second motor for cyclically controlling at a predetermined cycling rate the supply of air to the combustion process, reversing switch means, means connecting said second motor means in cyclical operative relation to said reversing switch means, said switching means being cycled at said predetermined rate, electrical connection means including said reversing switch means for connecting said second winding of the reversible motor means to said source of voltage so that the phase of the voltage that is applied to said winding will ce cyclically reversed, a balanceahle electrical network circuit having an output, a temperature rf'- sponsive impedance element responsive to the temperature of the combustion process, teroperature responsive element being connected in one leg of said network circuit, a variable iin-- pedance connected in an adjacent leg of said network circuit, slow operating third motor means, means connecting the output of said balanceahle electrical network in controlling relation to said third motor means, said third motor means being connected in operative relation to said variable egccefsi impedance so that upon the Vvunbalance of :said

circuit at a rate slower 'than the rate of unlca'l` ance of said network circuit caused by the eiect of said cyclical supply oi air to the combustionprocess upon said temperature Vresponsive lelement relay means, additional electrical connection' means including said relay means for connecting the output 'ofV the network vvcircuit rincontrolling relation to said rst vwinding of the reversible mctor vmeans so that upon an `increasing temperature of the combustion process resulting fircm the cyclical increase-in air supply, said reve-rsible vmotor 'meanswill increase the amount of air flowing to the combustion process.

6. In control apparatus for controlling the relative supplies ,of fuel and air to a combustion process, means for controlling the supply of fuel, means including reversible Amotor Vmeans for variably controlling the supply of air, means including motor means for cyclically varying the proportional supplies or" fuel and air, a balanceable electrical network circuit, said network cir-- cuit having an output, said network circuit cluding a .temperature responsive meansjresponsive to the temperature or the combustion process connected in one leg of the circuit, said circuit also including a variable impedance means connected in an adjacent leg oi said network circuit, slow operating motor means for adjust# ing said variable impedance means, means connecting said output in controlling relation to said slow operating motor means sov that upon the unbalance of said network circuit said slow operating motor means will adjust said impedance in a manner to effectively rebalance said network circuit means, relay means,A electrical connection means including said relay means for connecting the output of said electrical network circuit in controlling relation to said reversible motor means, and reversing switch means for reversing the operation of said reversible motor means.

'7. In control apparatus for controlling the relative supplies of combustion supporting materials to a combustion process, means for controlling the supply of one of said materials, means including reversible motor means for variably controlling the supply of another of said ma-v terials, means for cyclically varying the supply of one of said materials relative to the supply of 'the other of said materials, a balanceable netl work circuit means, said circuit including temperature responsive means having an electrical operate to vary said impedance in a manner to l restore the balance of said network circuit, relay means, reversible switching means, electrical connection means including said relay means for connecting said network circuit means in controlling relation to said reversible motor means, and further electrical means connecting said switching means in'controlling relation to said reversible motor means.

8. In control apparatus for controlling the relative supplies of combustion supporting materials to a combustion process, means for controlling the supply of one of said materials, means for controlling the supply of another of said materials, -means for .cyclically varying ata predetermined Vrrate 'the Vsupply of one of said materials relative to the supply'of the other of said materials, balanceable means-having atemperature responsive element sensitive to the tem-'- perature of said combustion .process and yalso including a relatively slew acting recalancing member for adjusting said balanceable rmeans to a state of'equilibrium when a change in temperature of said .combustion process causes an unbalance, driving means for operating said means -ior controlling the supply oi another of said materials, vconnection means. operatively connecting said balanceable means in controlling relation to said ldriving means, and reversing means for reversing at said predeterminedrate the effect of said balanceable means on said driving means.

19. In control vapparatus for controlling the relative supplies of fuel and airto a combustion process to maintain ythe temperature of the combustion processat Va finaximumvalue, means for controlling the supply of fuel to the combustion process, means for controlling the supply of air te the combustion process, first motor means for cycling at a predetermined' rate said means vfor controlling-the supply of air 'to the combustion process, balanceable means including a temperature responsive member and a rebalancing-meinber, said temperature response member being responsive to the temperature oi said combustion process and capable of unbalancing said balanceable means upon a change in the temperature of said combustion process, relatively slow driving means responsive to the unbalance of said balanceable means connected in controlling rela-- tion to said rebalancing member for rebalancing lsaid balanceable means, second motormeans responsive to the unbalance of said balanceable means for additionally controlling said means for controlling the supply of air tothe combustion process, and reversing means connected to said second motor means for reversing the eiect Aof* said balanceable means on said second mo- `supply of the other of said materials, balanceable means having a responsive element sensitive to the output of said process and also including a slow acting rebalancing member for adjusting said balanceable means to a state or equilibrium when a change in the output of said process causes an unbalance, means connectingsaid'balanceable means in controlling' relationto said phase sensitive actuatorV means, electrical reversible switching means, and means connecting said electrical switching means to said phase sensitive-actuator in such a manner that when the cycling of the supply of one of said materials relative to the supply of the other of said materials results in a cyclic change in the output of the process having the same phase the supply of said one of the materials will be increased.

11. In control apparatus for controlling the relative supplies of fuel and air to a combustion process, means for controlling the supply of fuel, means including a phase sensitive actuator means for controlling the proportional supplies of fuel and air, means for cyclically controlling at a predetermined rate the supply of air, a balanceable electrical network circuit, a temperature responsive impedance element responsive to the temperature of said process connected in one leg of said network circuit, a variable impedance connected in an adjacent leg of said network circuit, slow operatinglmotor means responsive to the unbalance of said network circuit for adjusting said variable impedance to rebalance said network circuit, means connecting said` network circuit in controlling relation to said phase sensitive actuator means, and reversing means connected to said phase sensitive actuator means.

12. In control apparatus for controlling the relative magnitudes of at least two variables affecting a process to maintain the output of the process at a maximum, means for controlling the magnitude of one of said variables, means including electrical phase sensitive actuator means for variably controlling the supply of another of said variables, means for cyclically varying at a predetermined rate the magnitude of one of said variables relative to the magnitude of the other of said variables, balanceable means having a responsive element sensitive to the output of said process and also including a slow acting r'ebalancing member for adjusting said balanceable means to a state of equilibrium when a change in the output of said process causes an unbalance, means connecting said balanceable means in controlling relation to said phase sensitive actuator means, electrical control means, and means connecting said electrical control means to said phase sensitive actuator in such a, manner that when the cycling of the magnitude of one of said variables relative to the magnitude of the other of said variables results in a cyclic change in the output of the process having the same phase, the magnitude of said one of the variables will be increased.

WALDO H. KLIEVER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,052,375 Wunsch Aug. 25, 1935 2,148,491 Moore Feb. 28, 1939 2,220,028 Smith Oct. 29, 1940 2,275,317 Ryder Mar. 3, 1942 2,352,143 Wills June 20, 1944 

